Study On The Influence Of Graphene Sheet Diameter On The Mechanical Properties Of Cementitious Materials

With the proposal of China’s "dual carbon" goal,the low-carbon and green cementitious materials have become a new development trend.On the basis of not reducing the mechanical properties of cement-based cementitious materials,effectively reducing their cement consumption is an important measure to help the construction field achieve the goal of carbon neutrality.At present,the mechanical properties of cementitious materials have been improved by adding graphene(Graphene Nanoplatelets(GNP),but the mechanism of action of GNP on cementitious materials has not been fully clarified.Based on this,the effects of GNP mixed with different sheet diameters and dosages on the working properties and mechanical properties of cement net slurry,cement mortar and concrete were studied,the optimal sheet diameter and dosage of GNP in the modification of cement-based cementitious materials were determined,and GNP was coated on coarse aggregate to form aggregate coating to prepare concrete,which further improved the mechanical properties of concrete,and the mechanism of action of GNP with different sheet diameters on cementitious materials was clarified through microscopic analysis.The main research contents are as follows:(1)In the cement paste and cement mortar system,GNP with different sheet diameters and dosages was mixed to obtain the influence law of its mechanical properties.At 28 d age,compared with the blank group,the compressive strength of GNP-2,GNP-4,GNP-7(2μm,4μ m,7 μ m)graphene modified cement slurry was 0.02%,0.02%,0.03% respectively Reached the maximum,increased by 18.0%,12.1%,and 9.0% respectively;the compressive strength of GNP-2,GNP-4,and GNP-7 graphene-modified cement mortar reached the maximum at 0.02%,0.03%,and 0.03% respectively,increased by 14.6%,12.1%,and 8.1%respectively;GNP-2,GNP-4,and GNP-7 graphene-modified cement mortar,the flexural strength reached the maximum at 0.02%,0.03%,and 0.03% respectively.Respectively increased by 18.2%,10.6%,6.1%.The research results show that GNP-2 has the most significant improvement on the mechanical properties of cement-based cementitious materials.(2)GNP with different sheet diameters and dosages was added to the cement net slurry and cement mortar system to obtain the law of its working performance influence.The net slurry flow of GNP-2,GNP-4 and GNP-7 graphene-modified cement with a dosage of 0.05%decreased by 8.5%,6.7% and 4.9%,respectively,compared with the blank group.The fluidity of GNP-2,GNP-4 and GNP-7 graphene-modified cement mortar decreased by 11.3%,10.3%and 7.7%,respectively.The water retention rates of GNP-2,GNP-4 and GNP-7graphene-modified cement mortar with a dosage of 0.05% were 97.66%,97.13% and 96.35%,respectively,which were improved compared with the blank group(95.52%).The results show that GNP-2 graphene has the most significant effect on the reduction of fluidity and water retention of cementitious materials.(3)The analysis of microscopic test results showed that GNP could promote the hydration degree and hydration rate of cementitious materials at 3d and 7d age,and the smaller the GNP sheet diameter,the more significant the hydration degree and hydration rate,while GNP had little effect on the hydration of cementitious materials aged 28 d.GNP can exert the filling effect and template effect,so that the pores are refined,and the hydration products are more dense and orderly.GNP has deflection,bridging and blocking effects on microscopic cracks,and can consume energy and disperse stress when subjected to external loads,thereby improving macroscopic mechanical properties.(4)The influence of GNP-coated aggregate concrete and conventional methods on mechanical properties and interface transition zone is proposed.The compressive strength and splitting tensile strength of GNP-2 modified concrete and GNP-2 coated aggregate concrete reached the maximum at 0.02% content.Compared with the blank group,the compressive strength of 28 d increased by 16% and 22.0%,respectively.The tensile strength of splitting increased by 8.5% and 12.7%,respectively.Compared with the blank group,the interface transition zone range of GNP modified concrete and GNP coated aggregate concrete was reduced by 40% and 60%,respectively.The microhardness of the interface transition zone increased by 12.3% and 29.4%,respectively.The results show that GNP-2 coated aggregate concrete has the most significant effect on improving mechanical properties and improving the interface transition zone.